A hybrid vehicle has an engine and a rotating electrical machine as drive sources. A power control device mounted on the hybrid vehicle includes a battery module, which includes a plurality of battery cells, and an inverter, which converts direct-current power output by the battery module to alternating-current power. For example, the inverter includes a semiconductor element for high power to increase the output and thus generates a large amount of heat due to power loss. The characteristics of the battery module greatly change depending on the temperature. Thus, an independent cooling system is separately provided for the power control device.
One such system for cooling a power control device adopts both water-cooling and air-cooling types. A water-cooling type cooling device cools an inverter. The water-cooling type cooling device includes a circulation path through which liquid cooling medium circulates, a pump for circulating the cooling medium, and a radiator for cooling the cooling medium. The radiator includes an electric fan arranged at a lateral face of the radiator to accelerate radiation of heat. An air-cooling type cooling device cools a battery module. The cooling device includes a motor-driven fan for sending air between battery cells.
Abnormality diagnosis for the cooling system needs to not only detect overheated states of the inverter and the battery module but also diagnose whether abnormality occurs when the ambient temperature is low. For example, when having a temperature in a low temperature range, a water temperature sensor arranged in the circulation path outputs the same detection signal as when having a broken wire. Thus, it is difficult to detect that the water temperature sensor in the low temperature range has a broken wire. Since the characteristics of the battery module change depending on the temperature, it is necessary to detect a state in which the inner temperature is significantly lower than the ambient temperature as well as detecting an overheated state. Thus, when the inner temperature becomes significantly lower than the ambient temperature, the battery module likely has some abnormality, and it is preferable to promptly detect the abnormality.
Patent Document 1 discloses a method for detecting a broken wire of a temperature sensor provided for a rotating electrical machine by using an ambient temperature and the like, which are detected by an ambient temperature sensor, and torque applied to the rotating electrical machine.